2021 wrx low on power with a low fuel tank

[Orangepeel]

Hey everyone last night I was driving home in my 21 wrx I had about 1/8th tank of fuel which i normally don’t let it get that low but I digress. It was low on power under acceleration and just lacked spunkiness in a noticeable way. I filled up with 93 octane fuel and it was immediately completely 100% better. I’ve never had a vehicle physically run different with a low tank of fuel. I don’t drive it every day and only get fuel a couple times a month. That being said maybe the fuel at the bottom wasn’t as good? I always run 93 and the fuel light wasn’t even on yet. Would you throw an additive in the tank? Obviously be more diligent to let it get that low. what do you guys think?

 

[ammolab]

Hey everyone last night I was driving home in my 21 wrx I had about 1/8th tank of fuel which i normally don’t let it get that low but I digress. It was low on power under acceleration and just lacked spunkiness in a noticeable way. I filled up with 93 octane fuel and it was immediately completely 100% better. I’ve never had a vehicle physically run different with a low tank of fuel. I don’t drive it every day and only get fuel a couple times a month. That being said maybe the fuel at the bottom wasn’t as good? I always run 93 and the fuel light wasn’t even on yet. Would you throw an additive in the tank? Obviously be more diligent to let it get that low. what do you guys think?

Your fuel pickup is always in the same place…the BOTTOM of the tank. You are always drawing fuel from the bottom of the tank. Full tank, last quart, all fuel is drawn From the same exact pickup location.

 

[Orangepeel]

Your fuel pickup is always in the same place…the BOTTOM of the tank. You are always drawing fuel from the bottom of the tank. Full tank, last quart, all fuel is drawn From the same exact pickup location.

Right so then the quality of whatever was left obviously was the issue…. At least one would assume.

 

[wpod]

Fuel economy mode???

 

[spasm3]

Fuel economy mode???

Interesting thought! Ecm programed to pull back power under 1/8 tank?

 

[kschachn]

Right so then the quality of whatever was left obviously was the issue…. At least one would assume.

Do you’re assuming you get quality stratification in the tank that persists during driving?

 

[twX]

I've never noticed this on my WRX. I do have a fuel injected motorcycle that seems to consistently make ~10-15% less power when the fuel level is low. I've always chalked it up to lower fuel pressure causing leaner AFRs and poor fuel atomization. Maybe the low volume of fuel in the tank becomes more aerated to the point that it affects fuel pump performance.

 

[atikovi]

My 18 Impreza was on E when I bought it. Drove fine for 3 miles to add gas. Drove the same after. Chalk it up to an isolated incident. Maybe a large amount of condensation in the tank was concentrated in the last 1/8 that went into the engine.

 

[Orangepeel]

My 18 Impreza was on E when I bought it. Drove fine for 3 miles to add gas. Drove the same after. Chalk it up to an isolated incident. Maybe a large amount of condensation in the tank was concentrated in the last 1/8 that went into the engine.

Something like this is what I am wondering.

 

[Orangepeel]

Do you’re assuming you get quality stratification in the tank that persists during driving?

In fairness I don’t know. Is it possible more moisture was at the bottom thus causing it to run like crap. It was noticeably off and when I filled up it was immediately fixed.

 

[someonesomewhere]

In fairness I don’t know. Is it possible more moisture was at the bottom thus causing it to run like crap. It was noticeably off and when I filled up it was immediately fixed.

Not saying it was water related, but the bottom is where the water goes when it stratifies. Gas floats on water.

 

[Marcozi]

Scan the engine computer to see what's going on.

 

[Orangepeel]

Scan the engine computer to see what's going on.

No codes

 

[ammolab]

In fairness I don’t know. Is it possible more moisture was at the bottom thus causing it to run like crap. It was noticeably off and when I filled up it was immediately fixed.

Not saying it was water related, but the bottom is where the water goes when it stratifies. Gas floats on water.

Read the second post in the thread

 

[Orangepeel]

Read the second post in the thread

What’s your point?

 

[KrisZ]

What’s your point?

The point is that if there is water in the tank, it doesn’t matter whether it’s full or near empty, the fuel pump will pump it regardless.

Since you admit you drive this car little, you likely had water in the fuel which got diluted and mixed when you filled up.

 

[Orangepeel]

The point is that if there is water in the tank, it doesn’t matter whether it’s full or near empty, the fuel pump will pump it regardless.

Since you admit you drive this car little, you likely had water in the fuel which got diluted and mixed when you filled up.

That’s pretty much what was said and then ammolab said to read the second post. We already figured that out I thought so I didn't know if there was another point being made…. Doesn’t seem like it though.

 

[ammolab]

What’s your point?

Point is: If there is water in your tank it will not be pumped out with the last gallon as the fuel pickup is always at the bottom of the tank….thus any water will go right to the bottom and be pumped out ASAP regardless of the level of fuel, full tank, half tank, 1/8th tank.

The quality of that last pint is no different than the first pint. You lost fuel pressure probably

 

[andreigbs]

Most likely scenario: since the fuel in the tank was so low, it progressively became hotter as the unburned fuel from the injection system returns back to the tank. The hotter the fuel itself becomes, the fuel temp sensor will instruct the ECU to pull back timing, resulting in lower power.

 

[Orangepeel]

Point is: If there is water in your tank it will not be pumped out with the last gallon as the fuel pickup is always at the bottom of the tank….thus any water will go right to the bottom and be pumped out ASAP regardless of the level of fuel, full tank, half tank, 1/8th tank.

The quality of that last pint is no different than the first pint. You lost fuel pressure probably

I can confirm via data log that pressure didn’t drop. Car still had 2.6gallons left.